Emile Horak

Exploratory use of Rigden Voids as Design Criteria for the Design of Sand Treated with Emulsion

ABSTRACT Soil/sand treated with emulsion (STE) sections were constructed experimentally by labour intensive and plant intensive means on sections at Marracuene, close to Maputo, Mozambique. No cement or lime was added as is standard practice in South Africa with emulsion treatment of gravels, but only bitumen emulsion. It was determined that the characteristics of the filler sized material (smaller than 75μm) in the soil/sand had significant influence on the performance of the sand asphalt pavements in the past. A laboratory study was launched to quantify the influence of the filler sized material in the STE mixes. Various Rigden voids determined filler binder ratios of mastic mixes were tested to determine the effect on Brookfield viscosity, Wilhelmi and normal ring and ball and ductility measurements. Rigden void filler-binder ratios were used in a reversal of criteria normally used with hot mix asphalt to determine stiffening of the mix. In a STE mix stiffening is due to the filler and binder combination as only emulsion is added to the sand or soil.

Forensic Investigation to Determine the Reasons for Premature Failure in an Asphalt Surface Layer: A Case Study

ABSTRACT Premature failure in the form of cracking, stripping and brittleness of a hot mix asphalt surfacing on a major road in South Africa was investigated. Anecdotal evidence as well as pavement structural evaluation with the FWD confirmed that the distress was restricted to the surface layer alone. Testing on the recovered binder indicated that excessive filler material was present in the mix. Testing of the filler included (laser) grading of filler, X-ray diffraction (XRD) tests, X-ray fluorescence spectrometry (XRFS) tests and an isotope dating test. It was found that prescribed addition of one percent lime was largely absent, which raised questions regarding the origin of the filler material. The filler was found to be super fine (average size 10 micrometer) and of mostly a tillite material origin. Rigden voids, viscosity, and softening point tests on the filler-binder mastic helped to quantify the stiffening effect of the filler. Binder film thicknesses were significantly reduced due to the surface area of the super-fine filler, which is linked to the observed brittleness, early cracking and stripping of the asphalt layer.

INVESTIGATION OF THE FOAMABILITY OF TAR AND THE CHARACTERISATION AND OPTIMISATION OF FOAMED TAR

ABSTRACT In southern Africa the scarcity of good road construction materials and long haulage distances have necessitated the use of methods to improve substandard materials or re-use by means of recycling. Tar is available in large quantities as a by-product of the fuel-from-coal process. The good adhesive properties of tar to aggregate are well known, but suitable construction processes limited the use of tar. Foamed bitumen (asphalt in the US) has been used extensively, and because of the low temperature application has major construction benefits. Due to the similarities in properties between bitumen and tar it was anticipated that tar could be used as a stabilising agent in the same manner as bitumen. The aim of the paper is to investigate the potential of foaming tar, and to present the key design parameters. The paper first presents the properties of tar, and specifically addresses the health considerations of low temperature carbo-tar which was the focus of this study. Thereafter the characterisation of foamed tar based upon the principles developed for foamed bitumen is presented. Foamed tar is investigated with respect to expansion ratio and half-life, and a new parameter known as the Foam Index. Optimisation methods for the foamability of tar are formulated with respect to the Foam Index, foaming temperature and foamant water content. Conclusions are drawn with regards to the tar foaming process and tentative limits are set with respect to the expansion ratio, half life and Foam Index necessary to achieve a satisfactory foamed tar stabilised material.

USE OF FOAMED TAR FOR CONSTRUCTION OF FLEXIBLE PAVEMENT WITH EXISTING UNPAVED ROAD STRUCTURE

Low-volume and unpaved roads constitute the majority of the road network throughout the developing and developed world. Upgrading these unpaved roads to conform to standards of low-volume flexible asphalt pavements is a costly exercise. In most instances, this involves constructing an entirely new pavement base. Recent technological advances in the field of deep in situ recycling have provided pavement engineers with an alternative to standard rehabilitation and reconstruction methods of flexible pavements. One such technique of stabilization is foamed tar treatment of inferior natural pavement materials through the application of deep in situ recycling to produce a stabilized base for lowvolume flexible pavements. Foamed tar technology and the concept of deep in situ recycling, and its advantages over current reconstruction methods, were reviewed. Health aspects relating to implementation of the stabilization process were addressed with respect to the use of gasifier tar in a controlled recycling environment. The engineering properties of foamed tar mixes were compared with existing stabilization techniques. A test section was constructed with particular attention to the flexibility of foamed tar for placement time, workability, and durability to environmental conditions. Performance testing results were analyzed. In conclusion, the benefits of foamed tar stabilization for developing an improved road network in a cost-effective manner were evaluated.